The present disclosure relates to a twin roll strip casting method, and more particularly, to a twin roll strip casting method for producing strips having a high degree of edge quality by using edge dams disposed on ends of casting rolls.
In a twin roll strip casting method of the related art, as illustrated in FIG. 1, molten steel 7 is dispensed through an injection nozzle (not shown) to a space between a pair of internal water-cooled rolls 1a and 1b that are rapidly rotated in mutually opposing directions, and a strip 5 having a thickness of 10 mm or less is extruded.
In the case of the twin roll strip casting method of the related art, two edge dams are attached to both ends of the pair of rolls 1a and 1b so as to prevent leakage of the molten steel 7. The pair of edge dams 10 may be seen as pressing devices disposed on the ends of the pair of rolls 1a and 1b to prevent leakage of the molten steel 7 from the space between the pair of rolls 1a and 1b past the ends of the pair of rolls 1a and 1b. During a casting process, a constant amount of back pressure is applied to the pair of edge dams 10 to maintain contact between the pair of edge dams 10 and the ends of the pair of rolls 1a and 1b. 
In this structure, molten steel 7 is supplied to a molten steel pool formed between the pair of rolls 1a and 1b and the pair of edge dams 10 while the pair of rolls 1a and 1b are rotated in mutually opposing directions, and the molten steel 7 is extruded through a nip between the pair of rolls 1a and 1b, thereby continuously producing a strip 5.
In general, portions of the edge dams 10 actually making contact with the pair of rolls 1a and 1b and thus wearing down may be formed of a material that easily wears down so that the portions of the edge dams 10 may gradually wear down as the pair of rolls 1a and 1b are rotated. That is, while the pair of rolls 1a and 1b are rotated, the pair of rolls 1a and 1b dig into particular portions of the edge dams 10, and thus, leakage of molten steel 7 is surely prevented. The particular portions of the edge dams 10 are commonly formed of a composite refractory material mixed with boron nitride (BN).
Referring to FIG. 2, edge dam reinforcing portions 12, configured to easily wear down, are portions of edge dams making contact with protruding portions of a pair of rotating rolls. Hereinafter, the protruding portions of the pair of rolls will be referred to as roll edges 2 for clarity of description.
The roll edges 2 and the edge dam reinforcing portions 12 are in close contact with each other, and as the pair of rolls are rotated in mutually opposing directions, the edge dam reinforcing portions 12, commonly formed of a refractory material, are subjected to continuous friction with the roll edges 2 of the pair of rolls and thus gradually wear down.
Therefore, regions of the edge dam reinforcing portions 12 that frequently contact and rub against the protruding roll edges 2 are gradually worn down and recessed from the other non-worn regions of the edge dam reinforcing portions 12. Therefore, the non-worn regions of the edge dam reinforcing portions 12 relatively protrude in the direction of the ends of the rolls, compared to the worn regions of the edge dam reinforcing portions 12.
In this case, molten steel contained in a molten steel pool is pushed by the relatively protruding non-worn regions of the edge dam reinforcing portions 12, and thus the width of a produced strip is unintentionally reduced.
Therefore, in a strip casting process of the related art, edge dams are lifted as casting proceeds, so as to prevent a decrease in the width of a strip when the edge dam reinforcing portions 12 wear down. In this case, the surface quality of products may be varied according to a method of lifting the edge dams, and thus the action of lifting the edge dams may have a direct effect on product quality.